ANN ARBOR, Mich.—Despite roller-coaster fuel prices, there are, in fact, plenty of folks who need a vehicle that can haul copious amounts of stuff and tow a trailer or camper as well. Last year GM debuted a pair a full-size sport utes—the GMC Yukon and Chevrolet Tahoe—with gas-electric hybrid powertrains that promised to offer all the expected capabilities in a more efficient package. If the EPA ratings of the 2WD GMC Yukon Hybrid model we tested—21 mpg city and 22 mpg highway—aren't earth-shattering, those figures represent a 31 percent improvement over nonhybrid versions. We did our own test with a 2WD Tahoe and recorded a 25 percent real-world improvement in fuel efficiency.

That's not bad, but we wondered how the hybrid SUV performs with a trailer attached. A recent, impulsive purchase of a 1973 Chevrolet Camaro Z28 provided a perfect excuse to test the Yukon Hybrid's hauling ability, because we had to tow the car approximately 200 miles from Indiana to Ann Arbor, Mich. Of course we were interested in the fuel economy, but we also wanted to know if the powertrain's normally transparent operation proved jerky or rough when asked to pull a significant load. Let's see how well this hybrid truck handles real work. —Larry Webster

The Specs

GM calls its hybrid a "two-mode hybrid" and that basically means that the truck can run purely on electric power or a combination of gas and electric propulsion. The guts of the system are housed in a transmission case that's roughly the same size as a conventional four-speed automatic. It's an innovative system that essentially combines the output of two 80-hp electric motors with a 332-hp 6.0-liter V8 through a transmission that uses both a CVT and four fixed ratios.

If it sounds complicated, that's because it is. We can't imagine the programming that went into the powertrain management system—"hybrid optimizing system" in GM-speak—that switches between the various motors and gearbox ratios and of course controls braking-energy recovery.

The hybrid system and the 300-volt battery pack add about 350 pounds, so GM took extra measures to reduce weight. The seats and wheels are lighter, and aluminum replaces steel for the hood, liftgate, front-bumper beam and the engine block. The diet paid off and the hybrid truck weighs about the same as the nonhybrid version, roughly 5900 pounds.

Other fuel-saving tricks include cylinder deactivation that can toggle the engine between V8 and V4 modes, variable cam timing, and several body modifications that reduce the drag coefficient from 0.36 to 0.34.

Our trailer, a wood-deck, open, single-car hauler, was brilliantly simple compared to the GMC, but it did have long aluminum ramps, which made loading the Camaro painless. The combination of the Z28 and the trailer weighed about 5000 pounds. That may be well under the Yukon Hybrid's 6200-pound tow rating, but it was more than enough to give the truck an adequate workout.

The Drive

A backup camera comes standard and it's one of several luxury items—like leather heated seats and a navigation system—that lessen the blow of the Yukon Hybrid's $50,945 base price. And we love backup cameras when it comes time to hook up a trailer because they make the task an easy, one-person job.

Once underway, the Yukon performed as smoothly and comfortably as it did unladen. The perceptive ones among us will notice a few unexpected and unfamiliar sensations, however. At stoplights, the gas engine shuts off, and it stays off for the first few dozen feet as the truck moves forward. At some point, the computer decides to start the engine. There's a slight shudder as the gas engine fires, but the transition is amazingly smooth. We only noticed the change in behavior because we were really looking for it. From there, the powertrain choreographs its own routine. At times, the vehicle speed rises, but engine rpm remains flat indicating the CVT is engaged. But as speed rises, there's the familiar feeling of fixed-gear upshifts.

We do have one small complaint: the brakes regenerate some of the hybrid's kinetic energy, which is great, but they feel a tad grabby. They're tricky to operate for smooth deceleration when towing.

The Bottom Line

Our 200-mile route was mostly on two-lane, 55-mph country roads with plenty of small-town stoplights. We'd call it more city driving than highway. Pulling the trailer, the Yukon Hybrid got 14.14 mpg. That seems a bit low for a hybrid. But we've never seen any better than 12 mpg while towing with a V8 powered truck in the past, so 14 mpg is nearly a 20 percent improvement. So we know the system has a positive impact on fuel economy. The trouble is, gas prices are now in a free fall, so many folks see little reason to spend an extra five grand to get the hybrid model. Dodge has killed the Durango Hybrid already, which means if you have large loads to haul and you want to do it as efficiently as possible, the GM hybrid line of trucks, which include pickups now too, is the only game in town.

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